This invention relates to a breathing apparatus and more particularly to a heat exchanger for use in a closed loop breathing apparatus for cooling the recycled gas.
Breathing apparatuses are generally of the open loop or the closed loop type. In the open loop type, compressed gas is delivered to the user and expired gas is vented to the atmosphere. Such systems are relatively simple and have the advantage of providing cool breathing gas to the user with a minimum of breathing resistance. However, since the gas is not recycled, a portable open loop breathing apparatus of reasonable weight has a relatively small supply of breathable gas available. In a closed loop breathing apparatus the exhaled gases are directed through a device which generates oxygen or at least removes carbon dioxide from the gas, which is then recycled to the user. Although some high pressure gas is normally supplied to the recycled gas, the high pressure gas tank can be relatively small and lightweight and still provide a breathing system which has a relatively long duration of air supply. Closed loop breathing apparatus systems, however, have the disadvantage that there is a significant buildup of heat in the recycled gas so that some means must be provided to remove at least a portion of the heat to make use of the system relatively move comfortable.
Prior art systems have provided a heat exchanger in the form of a jacket, coils or other means surrounding the high pressure gas tank and through which the recycled gas is passed in intimate contact with the exterior surface of the gas tank. As is well known, the flow of high pressure gas from the high pressure gas tank causes cooling of the tank so that there is a heat flow from the recycled gas to the tank through the heat exchanger. This type of heat exchanger permits only relatively slow heat flow so that the recycled air remains relatively warm.